KR20140071394A - Production of polycrystalline silicon by the thermal decomposition of silane in a fluidized bed reactor - Google Patents

Abstract

A method for producing polycrystalline silicon by thermal decomposition of silane is disclosed herein. The process of the present invention generally involves thermal cracking of the silane in a fluidized bed reactor operated at reaction conditions which provides a higher rate of productivity than conventional processes.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for producing polycrystalline silicon by thermal decomposition of silane in a fluidized bed reactor,

Cross reference of related application

This application claims benefit of U.S. Provisional Application No. 61 / 541,644 filed on September 30, 2011, the disclosure of which is incorporated herein by reference in its entirety.

Background technology

Field of the present disclosure relates to a process for producing polycrystalline silicon by thermal decomposition of silanes and to a process for the production of polycrystalline silicon in a fluidized bed reactor operating at a reaction condition which provides a higher rate of productivity, Lt; RTI ID = 0.0 > thermal < / RTI >

Polycrystalline silicon is an essential raw material used to make many commercial products including, for example, integrated circuits and photovoltaic cells (i.e., solar cells). Polycrystalline silicon is often produced by a chemical vapor deposition mechanism that deposits silicon on silicon particles from a thermally decomposable silicon compound in a fluidized bed reactor. The seed particles continue to grow in size until they are discharged from the reactor as a polycrystalline silicon product (i.e., "granule" polycrystalline silicon). Suitable resolvable silicone compounds include, for example, silanes and halosilanes such as dichlorosilane and trichlorosilane.

In many fluidized bed reactor systems, and particularly in systems where the material from the fluid phase is chemically decomposed to form a solid material, such as in a polycrystalline silicon production system, the solid material may be deposited on the walls of the reactor. Wall adducts often alter the reactor geometry, which can degrade reactor performance. Also, a portion of the wall deposit can be released from the reactor wall and dropped to the bottom of the reactor. Often, the reactor system must be stopped to remove the adhered material. To prevent premature reactor breakdown, the adherends must be periodically etched from the reactor walls and the reactor must be cleaned, thereby reducing the productivity of the reactor. The etching operation can cause stresses to the reactor system due to thermal shock or thermal expansion or shrinkage difference, which can lead to cracking of the reactor walls, which requires reconstruction of the unit. These problems are particularly acute in fluid bed reactor systems used in the production of polycrystalline silicon. Previous efforts to reduce solid deposition on the reactor walls have resulted in a loss of reactor productivity (i. E., A low conversion of silane to polycrystalline silicon), which results in a relatively larger reaction zone to achieve the same productivity as conventional processes .

Thus, there is a continuing need for a method of making polycrystalline silicon that limits or reduces the amount of deposits on the reactor but provides improved productivity over conventional methods.

summary

One aspect of the disclosure is directed to a method of making polycrystalline silicon by thermal decomposition of silane in a fluidized bed reactor having a reaction chamber. The reaction chamber has a cross section through which the core region, the peripheral region and the feed gas pass. The fluidized bed reactor produces at least about 100 kg / hr of polycrystalline silicon per square meter of reaction chamber cross-section. A first feed gas containing silane is introduced into the core region of the reaction chamber. The reaction chamber contains silicon particles and the first feed gas contains less than about 80 vol% silane. The silane is thermally decomposed in the reaction chamber to deposit a significant amount of silicon on the silicon particles. A second feed gas is introduced into the peripheral region of the reaction chamber. The concentration of silane in the first feed gas exceeds the concentration in the second feed gas. The total concentration of silane in the feed gas fed into the reaction chamber is less than about 15% by volume. The pressure in the reaction chamber is at least about 3 bar.

Another aspect of the present disclosure relates to a method of making polycrystalline silicon by thermal decomposition of silane in a fluidized bed reactor having a reaction chamber and a distributor for distributing the gas into the reaction chamber. The reaction chamber has a cross section through which the core region, the peripheral region and the feed gas pass. The fluidized bed reactor produces at least about 100 kg / hr of polycrystalline silicon per square meter of reaction chamber cross-section. A first feed gas containing silane is introduced into the distributor to distribute the first feed gas into the core region of the reaction chamber. The reaction chamber contains silicon particles. The first feed gas contains less than about 80 vol% silane. The temperature of the first feed gas prior to introduction into the distributor is less than about 400 < 0 > C. The silane is thermally decomposed in the reaction chamber to deposit a significant amount of silicon on the silicon particles. A second feed gas is introduced into the distributor to distribute the second feed gas into the peripheral region of the reaction chamber. The concentration of silane in the first feed gas exceeds the concentration in the second feed gas. The pressure in the reaction chamber is at least about 3 bar.

Various modifications to the features described in connection with the above-mentioned aspects of the present disclosure exist. Additional features may also be introduced into the aspects of the present disclosure referred to above. These refinements and additional features may be present individually or in any combination. For example, various features discussed below in connection with any exemplary embodiment of the present disclosure, alone or in any combination, may be introduced into any of the above-mentioned aspects of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a fluidized bed reactor suitable for use in accordance with the method of the present disclosure, wherein the flow into and out of the reactor is indicated;
2 is a radial cross-sectional view of a reaction chamber of a fluidized bed reactor in which a core region and a peripheral region are shown;
3 is an axial cross-sectional view of a reaction chamber of a fluidized bed reactor, in which a reaction liner and reactor shell are shown.
Corresponding reference characters indicate corresponding parts throughout the figures.

details

According to embodiments of the present disclosure, the productivity of a fluidized bed reactor in which silane is thermally cracked to form polycrystalline silicon can be maintained or even improved in a manufacturing process adapted to reduce deposition of silicon deposits on the reactor walls Respectively.

Methods of reducing deposition of material on the reactor wall

In various embodiments of the present disclosure, a first feed gas comprising silane is introduced into the core portion of the reactor and a second feed gas having a lower silane composition than the first feed gas (e.g., , The formation of the silicon deposits on the reactor walls can be reduced by introducing them into the peripheral region of the fluidized bed reactor. Referring now to Figure 1, an exemplary fluidized bed reactor 1 for carrying out the method of the present disclosure is generally designated (1). The reactor (1) includes a reaction chamber (10) and a gas distribution unit (2). The first feed gas 5 and the second feed gas 7 are introduced into the distribution unit 2 so that each gas is distributed in the inlet of the reaction chamber 10. In this regard, it should be understood that, as used herein, "first feed gas" is a gas having a composition different from "second feed gas" and vice versa. The first feed gas and the second feed gas may consist of a plurality of gaseous compounds as long as the mass or molar composition of at least one of the compounds in the first feed gas is different from that of the compound in the second feed gas. The product recovery tube 12 extends through the gas distribution unit 2. The product particles can be recovered from the tube 12 and transported to the product reservoir 15. The reaction chamber 10 may include a freeboard region 11 that may have a larger radius than the lower region 13 and the lower region 13. [ The gas moves upward in the reaction chamber 10 and is introduced into the free board region 11. [ In the free board region 11, the gas velocity decreases and the entrained particles fall back into the lower region 13. The consuming gas 16 is discharged from the reactor chamber 10, which can be introduced into the further processing unit 18. The reaction chamber 10 is not partitioned into a separate portion near the reaction chamber wall (for example, a separate portion into which a small amount of silane or a silane-free feed gas is introduced) so that silicon deposition can occur It is preferable that the portion of the reaction chamber in which it is located is maximized. However, unless otherwise stated, the reaction chamber may include one or more such compartments without departing from the scope of the present disclosure. In this regard, it should be understood that the reactor 1 shown in FIG. 1 is exemplary and that other reactor designs can be used without departing from the scope of the present disclosure (e.g., Not a reactor).

2, which shows a cross-section of a fluidized bed reactor 1, the fluidized bed reactor 1 has a core region 21 extending from the center C of the reactor to the peripheral region 23. The peripheral region 23 extends from the core region 21 to the annular wall 25. The fluidized bed reactor 1 has a radius R extending from the center C of the reactor 1 to the annular wall 25. In various embodiments of the present disclosure, the core region extends from center C to less than about 0.975R, less than about 0.6R, and in other embodiments, less than about 0.5R or even less than about 0.4R. In these and other embodiments, the core region extends from center C to at least about 0.5R, at least about 0.6R, at least about 0.8R, or even at least about 0.9R. In this regard, it should be understood that fluidized bed reactor designs other than those shown in FIG. 2 may be used without departing from the scope of the present disclosure. Regardless of the cross-sectional shape of the fluidized bed reactor, the ratio of the surface area of the cross-section of the core region to the cross-sectional area of the peripheral region is less than about 25: 1, less than about 15: 1, less than about 10: Less than about 1: 3, less than about 1: 4, less than about 1: 5, or less than about 1:25 (e.g., less than about 4: 3 to about 1: 10 or about 1: 1 to about 1: 10).

As described above, the concentration of silane introduced into the core region 21 of the fluidized bed reactor 1 exceeds the concentration introduced into the peripheral region 23. The deposition of a material (e.g., silicon, etc.) on the reactor wall can be reduced by introducing the thermally decomposable compound (e.g., silane) into the interior portion of the reactor and further away from the reactor wall. In general, any method available to those skilled in the art may be used to direct the first feed gas into the core region of the fluidized bed reactor and the second feed gas into the peripheral region of the reactor. For example, as disclosed in U.S. Patent Application Publication No. 2009/0324479 and U.S. Patent Application Publication No. 2011/0158857, both of which are incorporated herein by reference for all relevant and consistent purposes, May be used. In this regard, it should be understood that other methods and apparatus may be used to obtain the desired gas distribution without departing from the scope of the present disclosure.

According to an embodiment of the present disclosure, the concentration of silane (by volume) in the first feed gas is at least about 25% higher than the concentration of silane in the second feed gas (e.g., the concentration of silane in the second feed gas Is about 10% by volume, the concentration in the first feed gas is at least about 12.5% by volume). In various other embodiments, the concentration (by volume) of silane in the first feed gas is at least about 35% higher than the concentration of silane in the second feed gas, or greater than the concentration of silane in the second feed gas At least about 50%, at least about 75%, at least about 100%, at least about 150%, or at least about 200% higher (e.g., from about 25% 200%, about 25% to about 100%, or about 50% to about 200% higher). In these and other embodiments, at least about 4% of the total amount of silane introduced into the fluidized bed reactor is introduced into the core region of the fluidized bed reactor where the remaining 96% is introduced into the surrounding region. In another embodiment, at least about 25%, at least about 50%, at least about 75%, at least about 85%, at least about 95%, or about 100% of the silane introduced into the fluidized bed reactor is introduced through the core region.

(1) maintaining the total concentration of silane in the feed gas introduced into the reaction chamber at less than about 15% by volume, and / or (2) introducing the second feed gas into the reactor By maintaining the temperature of the entire first feed gas below about 400 ° C, undesirable deposition of silicon in the fluidized bed reactor can be reduced. In this regard, as used herein, the phrase "total concentration " refers to the averaged concentration based on volume (i.e., typically, volume flow rate) when more than one gas is introduced into the reaction chamber.

In embodiments where the temperature of the first feed gas prior to introduction into the fluidized bed reactor is maintained at less than about 400 캜, the total concentration of silane introduced into the fluidized bed reactor may be relatively high, such as up to about 80% by volume of silane. In this embodiment, the total concentration of silane is less than about 60 vol%, less than about 40 vol%, less than about 20 vol%, less than about 15 vol%, less than about 10 vol%, less than about 5 vol% To about 80% by volume, from about 5% by volume to about 80% by volume, from about 5% by volume to about 25% by volume, or from about 2% by volume to about 20% by volume. Similarly, the concentration of the first feed gas and / or the second feed gas may be included within the ranges described above with respect to the total concentration of the gas. Also, the first feed gas prior to introduction into the distributor may be introduced into the distributor at lower temperatures, such as less than about 350 占 폚, less than about 300 占 폚, less than about 200 占 폚, or even less than about 100 占 폚. The second feed gas prior to introduction into the distributor may be introduced at a temperature of less than about 400 ° C, less than about 350 ° C, less than about 300 ° C, less than about 200 ° C, or even less than about 100 ° C. In some embodiments, particularly in embodiments where the second feed gas contains less than about 1 volume percent silane or less than about 1 volume percent thermally decomposable silicone compound, reducing the amount of external heat that must be applied to the reactor The second feed gas is introduced into the reactor at a relatively higher temperature than the first feed gas. For example, if the second feed gas has a temperature of at least about 100 占 폚, at least about 200 占 폚, at least about 300 占 폚, at least about 350 占 폚, at least about 450 占 폚, or even at least about 550 占 폚 About 300 DEG C to about 600 DEG C, or about 450 DEG C to about 600 DEG C).

In embodiments where the total concentration of silane in the feed gas introduced into the reactor is maintained at less than about 15% by volume, the temperature of the first and / or second feed gas prior to introduction into the distributor may be greater than about 400 < 0 & , Up to about 600 캜, such as from about 400 캜 to about 600 캜 or from about 500 캜 to about 600 캜). However, it is desirable to maintain the temperature of the first and / or second feed gas prior to introduction into the distributor below about 400 ° C or below about 350 ° C, below about 300 ° C, below about 200 ° C, or even below about 100 ° C Do. In embodiments where the total concentration of silane in the feed gas is maintained at less than about 15% by volume, the concentration of silane in the first feed gas may be less than about 80% by volume. In another embodiment, the first feed gas comprises less than about 60 vol%, less than about 40 vol%, less than about 20 vol%, less than about 15 vol%, less than about 10 vol%, less than about 5 vol% To about 80 vol%, about 5 vol% to about 80 vol%, about 5 vol% to about 25 vol%, or about 2 vol% to about 20 vol% silane. The remainder of the first feed gas and / or the second feed gas may be a carrier gas, such as a compound selected from the group consisting of silicon tetrachloride, hydrogen, argon and helium. In these and other embodiments, the second feed gas comprises less than about 15 vol% silane, or less than about 10 vol%, less than about 5 vol%, less than about 3 vol%, less than about 1 vol% About 15 vol.%, Or about 1 vol.% To about 5 vol.% Silane. In this regard, it should be understood that the second feed gas may comprise a gas other than silane (i.e., it may not contain silane). For example, the second feed gas may be based on one or more compounds selected from the group consisting of silicon tetrachloride, hydrogen, argon, and helium (e.g., containing only these compounds and other small amounts of other gaseous impurities) ). Also in this regard, the second feed gas may consist of one or more compounds selected from silicon tetrachloride, hydrogen, argon and helium.

Depending on the desired inlet temperature of the first feed gas and the second feed gas, the first feed gas and / or the second feed gas may be heated prior to introduction into the reactor, and the first and / or second feed gas In embodiments comprising gas recycled from another process stream, the first and / or second feed gas may be cooled. Any heating or cooling method known to those skilled in the art can be used, including the use of indirect steam or electric heating and / or the use of combustion gases and indirect cooling by cooling the liquid (e.g., water or molten salt).

As the silane is introduced into the reaction chamber 10 and heated, it is thermally decomposed according to the following reaction formula to produce polycrystalline silicon and hydrogen.

<Reaction Scheme 1>

SiH ₄ ? Si + 2H ₂

In this connection, reactions other than the reaction scheme 1 shown above can occur in the reaction chamber 10, and the reaction scheme 1 is not regarded as having a limited meaning; It should be understood that Scheme 1 may represent most of the reactions taking place in the reaction chamber.

How to Maintain Proper Reactor Productivity

It has been found that one or more of the following methods can be used to maintain acceptable productivity or even to improve productivity compared to conventional manufacturing methods when using the method described above for reducing the deposition of material on the reactor walls (1) the pressure of the fluidized bed reactor can be controlled to within a certain range as described below, (2) the first and second fluidized gases can be rapidly heated in the reaction chamber to promote deposition of the polycrystalline silicon, And / or (3) the diameter of the recovered polycrystalline silicon microparticles can be controlled within a specific range as described below.

In certain embodiments of the present disclosure, the absolute pressure in the fluidized bed reactor is at least about 3 bar. By maintaining the pressure in the fluidized bed reactor above about 3 bar, sufficient reactor productivity has been shown to be achievable. In general, significantly higher pressures may be used (e.g., up to about 25 bar); High pressures may be less desirable because such pressure may include the application of relatively high external heat through the reactor walls (e.g., higher temperatures) and may result in unacceptable amounts of silicon deposition on the reactor walls. In certain embodiments, the pressure of the reactor is at least about 4 bar, at least about 5 bar, at least about 10 bar, at least about 15 bar, at least about 20 bar, or even at least about 25 bar (e.g., from about 3 bar to about 25 bar bar or about 4 bar to about 20 bar).

In this regard, it should be appreciated that the pressure of the reactor typically decreases as the gas passes through the reactor. In view of this change, the pressure of the reactor can be measured near the gas outlet to ensure that a minimum pressure (e.g., about 3 bar) is achieved. In certain embodiments of the present disclosure, the pressure of the consuming gas discharged from the reactor is measured to ensure that the fluidized bed is operated within the stated pressure range. For example, the pressure of the consuming gas may be at least about 3 bar, at least about 4 bar, at least about 5 bar, at least about 10 bar, at least about 15 bar, at least about 20 bar, or even at least about 25 bar 3 bar to about 25 bar or about 4 bar to about 20 bar).

As described above, the temperature of the first feed gas and / or the second feed gas introduced into the fluidized bed reactor may be less than about 400 ° C. It has been shown that the productivity of the fluidized bed reactor can be increased by rapid heating of the incoming gas. 3, where a reaction chamber 10 of a fluidized bed reactor is shown, according to one or more embodiments of the present disclosure, a heating device 34 of the fluidized bed reactor is connected to the reaction liner 32 (i. E., The reaction chamber wall) And an outer shell 35 of the reactor. By placing the heating device 34 inside the outer shell 35, the heat is not guided through both the outer shell 35 and the liner 32 to reach the contents of the reaction chamber so that the heating device can be operated at a low temperature have. This configuration allows relatively rapid heating to be achieved and avoids the use of a hot gradient across the reactor which limits the material that can deteriorate the reactor material and that can be used to form the outer shell 35.

The heating device 34 may be an electric resistance heater or one or more induction coils; Other types of heating devices may be used without limitation (e.g., the heating device 34 may be a heating gas, such as a combustion gas). The liner 32 may be made from any material suitable for the operation of a fluidized bed reactor and also for the production of granular polycrystalline silicon, and more particularly a material which is sufficiently resistant to etching and deterioration which may lead to contamination of the polycrystalline silicon product. Suitable materials include, for example, quartz, graphite coated with or coated with silicon carbide, silicon carbide coated with silicon, and zinc and tantalum alloys. The outer shell 35 may be made of any number of metallic materials (e.g., a metal alloy including carbon steel or stainless steel).

In various embodiments, a gas 38 (e.g., argon, hydrogen, nitrogen, and / or helium) may be included in the inner chamber 39, which is preferably continuously introduced into and withdrawn from the inner chamber. The base 38 serves to protect the heating device 34 from depositing silicon on the various outer surfaces due to leakage into the inner chamber 39 through the reaction liner 32. The gas 38 can be maintained at a pressure below the pressure of the process gases 5 and 7 so that when the liner 32 forms an opening (e.g., crack or pin-hole) Passing through the liner 32 to prevent introduction of gas 38 into the reaction chamber, thereby avoiding movement of contaminants into the reaction chamber. In embodiments where the liner 32 is made of quartz (and more particularly, it is quartz-based), the differential pressure between the base 38 and the process gases 5, It is possible to avoid the collapse of the movable member 32. For other materials, it may be advantageous to keep the pressure of the gas 38 above about 1 bar and below the pressure of the process gases 5, 7 to prevent contamination into the reaction chamber through the liner 32. At least about 5 bar, at least about 10 bar, at least about 15 bar, or at least about 20 bar or more and a process gas (5), (7) pressure less than about 1 bar, at least about 1.1 bar, (E.g., from about 1 bar to about 20 bar, from about 1.1 bar to about 20 bar, from about 1 bar to about 20 bar, or from about 5 bar to about 20 bar). In this regard, the upper limit for the pressure drop can be determined based on the structural integrity of the reactor wall, which will also be influenced by the constituent material, wall thickness and reactor diameter.

In general, the reaction chamber 10 of a smaller diameter can withstand a larger pressure difference. However, larger diameter reaction chambers may be desirable to achieve greater throughput through the reactor. In some embodiments, the diameter of the reaction chamber 10 may be at least about 10 inches, at least about 20 inches, at least about 30 inches, or at least about 40 inches or more.

In addition, the base 38 may be maintained at a temperature below the process gases 5, 7 to prevent corrosion. It is also possible to monitor the presence of a process gas (e.g., silane) as the substrate 38 is recovered from the inner chamber 39 and thereby detect the presence of a liner 32 in the opening (e.g., Holes) are formed, and that maintenance may also be required. The inner chamber 39 (or portion thereof) may include insulating material to prevent heat loss. The insulation used may be any material suitable for insulating at elevated temperatures (both carbon and inorganic), as will be appreciated by those skilled in the art, and may have a variety of shapes including insulating blocks, blanket or felt .

Examples of fluidized bed reactors for use in accordance with this disclosure are disclosed in U.S. Patent Application Publication No. 2008/0299291, U.S. Patent Application Publication No. 2008/0241046, and U.S. Patent Application Publication No. 2009/0095710, each of which is incorporated herein by reference for all relevant and consistent purposes Incorporated herein by reference). In this regard, it should be understood that reactor designs other than those shown in FIG. 3 and other than those described in the cited publications may be used without departing from the scope of the present disclosure.

The first feed gas and the second feed gas are heated as they are introduced into the fluid bed reactor and are continuously heated as they rise in the reaction chamber. The reaction gas may be heated to at least about 500 캜 before being discharged from the reaction chamber (or quenched as described below), and in yet another embodiment to at least about 600 캜, to at least about 650 캜, to at least about 700 캜 , To at least about 750 占 폚, from about 600 占 폚 to about 800 占 폚, or from about 700 占 폚 to about 800 占 폚.

As shown in FIG. 1, the particulate polycrystalline silicon is recovered from the product recovery tube 12. The particulate polycrystalline silicon can be recovered intermittently from the reactor as in a batch operation; It is preferred that the particulate product is continuously recovered. Regardless of whether batch or continuous recovery of the silicon product was used, the size of the product particles upon recovery from the reactor was found to affect reactor productivity. For example, it has been shown that increasing the size of recovered silicon particulate generally increases reactor productivity; If the product particles are excessively grown, the contact between the gas in the reactor and the solid phase can be reduced and productivity can be reduced. Thus, in various embodiments of the present disclosure, the average diameter of the particulate polycrystalline silicon recovered from the reactor is from about 600 microns to about 2000 microns, or from about 800 microns to about 1300 microns. In this regard, it should be understood that reference to the average diameter of the various particles herein refers to the Sauter mean diameter, unless otherwise stated. Sauter mean diameter can be measured according to methods generally known to those skilled in the art.

Even in embodiments in which one or more of the above-described methods are used, and even more than one method is used to reduce the deposition of material on the reactor walls as described above, it may be possible to maintain relatively high reactor productivity. As will be appreciated by those skilled in the art, reactor productivity can be expressed as a percentage of polysilicon production per reactor chamber cross-sectional area. According to the present disclosure, at least about 100 kg / hr of silicon per square meter of reaction chamber cross-section is deposited on the silicon particles in the reactor when more than one of the above-mentioned methods for increasing reactor productivity is used. At least about 150 kg / hr, at least about 250 kg / hr, at least about 300 kg / hr, at least about 500 kg / hr, at least about 700 kg / hr, at least about 1000 at least about 2000 kg / hr, at least about 3000 kg / hr, at least about 4000 kg / hr or about 100 kg / hr to about 5000 kg / hr, at least about 250 kg / hr to about 5000 kg / 100 kg / hr to about 4000 kg / hr or about 100 kg / hr to about 1000 kg / hr of silicon is deposited on the silicon particles.

In this regard, in embodiments where the cross-section of the reaction chamber varies along the length of the reactor, the cross-sectional area referred to is the cross-sectional area averaged over the length of the reaction chamber (e.g., the length of the reaction chamber where at least about 90% As used herein. It is also to be understood that the reactor may have ubiquitous regions whose productivity is higher or lower than the stated value, without departing from the scope of the present disclosure.

Other parameters for the operation of the fluidized bed reactor

Silicon seed particles are added to the reactor to provide a surface on which polycrystalline silicon can be deposited. The seed particles continue to grow in size until they are discharged from the reactor as a particulate polycrystalline silicon product. The seed particles can be added to the reactor batchwise or continuously. The average diameter of the crystal seed particles (i.e., the Sauter mean diameter) may be from about 50 microns to about 800 microns, and in some embodiments, from about 200 microns to about 500 microns. The source of the silicon seed particles comprises small polycrystalline silicon particles that are aggregated and separated from the product particles and / or the granular polycrystalline product collected from the reactor pulverized to the desired size.

During operation of the fluidized bed reactor system, the fluidized gas velocity through the reaction zone of the fluidized bed reactor is maintained above the minimum fluidization rate of the polycrystalline silicon particles. The gas velocity through the fluidized bed reactor is generally maintained at a rate of about 1 to about 8 times the minimum fluidization velocity necessary to fluidize the particles in the fluidized bed. In some embodiments, the gas velocity is from about 1.1 to about 3 times the minimum fluidization velocity necessary to fluidize the particles in the fluidized bed. The minimum fluidization rate depends on the nature of the gas and particles involved. The minimum fluidization rate can be measured by conventional means (see p. 17-4 of Perry's Chemical Engineers' Handbook, 7th Ed., Incorporated herein by reference for all relevant and consistent purposes). Although the present disclosure is not limited to any particular minimum fluidization rate, the minimum fluidization rate useful in the present disclosure ranges from about 0.7 cm / sec to about 250 cm / sec, or even from about 6 cm / sec to about 100 cm / sec . The average gas residence time for the gas introduced into the reaction chamber is less than about 20 seconds, or in other embodiments, less than about 12 seconds, less than about 9 seconds, less than about 4 seconds, less than about 1 second, It can be 20 seconds.

In order to achieve higher productivity, and also to prevent local de-fluidization, higher gas velocities than the minimum fluidized flow are often desired. As the gas velocity increases beyond the minimum fluidization velocity, the excess gas forms bubbles and the bed voidage is increased. The layer may be considered to consist of an "emulsion" containing a gas contacted with bubbles and silicon particles. The properties of the emulsion are very similar to those of the layer at the minimum fluidization conditions. The local porosity in the emulsion is close to the minimum fluidized bed porosity. Thus, bubbles are generated by the gas introduced in excess of what is needed to achieve minimum fluidization. As the ratio of the actual gas velocity to the minimum fluidization velocity increases, bubble formation is enhanced. At a very high rate, large slugs of gas are formed in the layer. As the bed porosity increases with the total gas flow rate, the contact between the solid and the gas becomes less effective. At a given layer volume, the surface area of the solid in contact with the reactive gas decreases as the layer porosity increases, which results in a reduced conversion rate to the polycrystalline silicon product. Thus, the gas velocity must be adjusted to maintain decomposition within an acceptable level.

1, the reaction chamber 10 of the fluidized bed reactor 1 is also provided with a reaction chamber 10 for reducing the velocity of the fluidizing gas and for allowing the particulate material to be separated from the gas. In some embodiments of the present disclosure, And a "freeboard" area 11 of increased diameter. In this regard, in embodiments where the reactor comprises a freeboard region, this region is considered to be part of the reaction chamber (for example, for measurements of the reactor's mean radius, residence time, etc.) I must understand. In order to reduce the formation of silicon dust and also to reduce the deposition of silicon at the outlet of the reactor and in the freeboard region by reducing the temperature of the exhaust gas from the reactor the quenching gas into the freeboard region of the reactor (E. G., Silicon tetrachloride, hydrogen, argon and / or helium). Suitable methods of using such quenching gases are described in U.S. Pat. No. 4,868,013, which is incorporated herein by reference for all relevant and consistent purposes. The temperature and flow rate of the quenching gas is such that the temperature of the exhausted consumer gas is less than about 500 캜, and in yet another embodiment, less than about 400 캜, less than about 300 캜, from about 200 캜 to about 500 캜 or from about 200 캜 to about 400 캜 Lt; / RTI &gt; The temperature of the quenching gas may be less than about 400 DEG C, less than about 300 DEG C, less than about 200 DEG C, or less than about 100 DEG C (e.g., from about 10 DEG C to about 400 DEG C, from about 10 DEG C to about 300 DEG C, 400 &lt; 0 &gt; C). The weight ratio of process gas to quenching gas introduced into the reactor may be from about 20: 1 to about 700: 1 or from about 50: 1 to about 300: 1.

In some embodiments of this disclosure, the conversion of silane in the fluidized bed reactor is at least about 20%, at least about 40%, at least about 50%, at least about 80%, at least about 90%, at least about 95%, or even at least about (E.g., from about 80% to about 100%, from about 90% to about 99%, from about 80% to about 99%). In this regard, it should be understood that the conversion rate may vary depending on many factors, including reactor design and operating parameters (temperature, pressure, etc.).

Example

Example 1: Modeling of polycrystalline silicon from silane decomposition in a two-gas high pressure fluid bed reactor

The production of polycrystalline silicon by thermal decomposition of silane in a high-pressure fluidized-bed reactor, feeding hydrogen into the peripheral region of the reaction chamber and introducing silane-containing gas into the core of the reaction chamber, is accomplished by computational fluid dynamics (CFD) Software. The total silane concentration in the gas fed into the reactor was maintained at 2% by volume. The gas introduced into the core region of the reactor contained 4.8% by volume and was introduced into the core region at a temperature of 395 ° C. The gas introduced into the peripheral region of the reactor contained no silane and was introduced into the reactor at a temperature of 600 ° C. The ratio of the surface area of the core area of the reaction chamber to the surface area of the peripheral area was 1: 2. The pressure of the reactor gas outlet was maintained at 20 bar (absolute) and the reaction chamber was maintained at 700 ° C. The modeled data indicated that the silane conversion rate was 99.9%. The productivity of this simulated reactor is 180 kg / hr of polycrystalline silicon per square meter of reaction chamber cross section.

When introducing elements of this disclosure or its preferred embodiment (s), the articles "a", "an", "the" and "said" are intended to mean that there is more than one element. The terms " comprising, "" including," and "having" are intended to be inclusive and mean that there may be additional elements other than those listed.

It will be understood that, since various changes may be made in the above apparatus and methods without departing from the scope of the present disclosure, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense Is intended.

Claims (40)

1. A method for producing polycrystalline silicon by thermal decomposition of silane in a fluidzed bed reactor having a reaction chamber, the reactor having a core region, a peripheral region and a cross section through which the feed gas passes, Producing at least about 100 kg / hr of polycrystalline silicon per square meter of chamber cross-section,
Introducing a first feed gas comprising silane into the core region of the reaction chamber, the reaction chamber containing silicon particles, the first feed gas containing less than about 80 vol% silane, Thermally decomposing in the reaction chamber to deposit a certain amount of silicon on the silicon particles; And
Introducing a second feed gas into the peripheral region of the reaction chamber wherein the concentration of silane in the first feed gas exceeds the concentration in the second feed gas and the concentration of silane in the feed gas fed into the reaction chamber The total concentration is less than about 15% by volume, and the pressure in the reaction chamber is at least about 3 bar.
&Lt; / RTI &gt; The method according to claim 1,
Wherein the reaction chamber has an annular wall and has a generally circular cross-section with a center and a radius, R, wherein the core region is less than about 0.975R, less than about 0.6R, less than about 0.5R, Less than about 0.4 R, at least about 0.5 R, at least about 0.6 R, at least about 0.8 R, or at least about 0.9 R, said peripheral region extending from said central region to said annular wall. 3. The method according to claim 1 or 2,
Wherein the temperature of the first feed gas prior to introduction into the reaction chamber is less than about 400 ° C, less than about 350 ° C, less than about 300 ° C, less than about 200 ° C, or less than about 100 ° C. 4. The method according to any one of claims 1 to 3,
Wherein the temperature of the second feed gas prior to introduction into the reaction chamber is less than about 400 占 폚, less than about 350 占 폚, less than about 300 占 폚, less than about 200 占 폚, or less than about 100 占 폚. 5. The method according to any one of claims 1 to 4,
Wherein the temperature of the second feed gas is at least about 300 캜, at least about 350 캜, at least about 450 캜, at least about 550 캜, from about 300 캜 to about 600 캜, or from about 450 캜 to about 600 캜. 6. The method according to any one of claims 1 to 5,
The pressure in the fluidized bed reactor is at least about 4 bar, at least about 5 bar, at least about 10 bar, at least about 15 bar, at least about 20 bar, at least about 25 bar, from about 3 bar to about 25 bar, bar, method. 7. The method according to any one of claims 1 to 6,
At least about 4 bar, at least about 5 bar, at least about 10 bar, at least about 15 bar, at least about 20 bar, at least about 25 bar , From about 3 bar to about 25 bar, or from about 4 bar to about 20 bar. 8. The method according to any one of claims 1 to 7,
Wherein the volume based concentration of silane in the first feed gas is at least about 25% higher than the volume based concentration of silane in the second feed gas, or a volume based concentration in the first feed gas At least about 50%, at least about 75%, at least about 100%, at least about 150%, at least about 200%, or from about 25% to about 200%, from about 25% to about 100 %, Or from about 50% to about 200% higher. 9. The method according to any one of claims 1 to 8,
At least about 25%, at least about 50%, at least about 75%, at least about 85%, at least about 85%, or at least about 80% of the silane introduced into the fluidized bed reactor, At least about 95%, or about 100%, is introduced through the core region. 10. The method according to any one of claims 1 to 9,
Wherein particulate polycrystalline silicon is recovered from the fluidized bed reactor and wherein the particulate polycrystalline silicon has a Sauter mean diameter of from about 600 microns to about 2000 microns or from about 800 microns to about 1300 microns. 11. The method according to any one of claims 1 to 10,
Wherein the average residence time of the gas introduced into the reaction chamber is less than about 20 seconds, less than about 12 seconds, less than about 9 seconds, less than about 4 seconds, less than about 1 second, or about 0.1 seconds to about 20 seconds. 12. The method according to any one of claims 1 to 11,
At least about 150 kg / hr of silicon per square meter of reaction chamber cross-section is deposited on the silicon particles, or at least about 250 kg / hr, at least about 300 kg / hr, at least about 500 kg at least about 1000 kg / hr, at least about 2000 kg / hr, at least about 3000 kg / hr, at least about 4000 kg / hr or about 100 kg / hr to about 5000 kg / hr, From about 250 kg / hr to about 5000 kg / hr, from about 100 kg / hr to about 4000 kg / hr, or from about 100 kg / hr to about 1000 kg / hr of silicon is deposited on the silicon particles. 13. The method according to any one of claims 1 to 12,
Wherein the second feed gas comprises less than about 15 vol% silane, less than about 10 vol%, less than about 5 vol%, less than about 3 vol%, less than about 1 vol%, about 1 vol% to about 15 vol% By volume to about 5% by volume silane. 14. The method according to any one of claims 1 to 13,
Wherein the second feed gas essentially comprises compounds other than silane. 14. The method according to any one of claims 1 to 13,
Wherein the second feed gas essentially comprises at least one compound selected from the group consisting of silicon tetrachloride, hydrogen, argon and helium. 16. The method according to any one of claims 1 to 15,
Wherein the first feed gas comprises less than about 60 vol% silane, less than about 40 vol%, less than about 20 vol%, less than about 15 vol%, less than about 10 vol%, less than about 5 vol%, about 2 vol% From about 5 vol% to about 80 vol%, from about 5 vol% to about 25 vol%, or from about 2 vol% to about 20 vol% silane. 17. The method according to any one of claims 1 to 16,
The total concentration of silane in the feed gas introduced into the reaction chamber may be less than about 12 vol% or less than about 8 vol%, about 1 vol% to about 15 vol%, about 1 vol% to about 10 vol%, about 5 vol% To about 15% by volume, or from about 10% by volume to about 15% by volume. 18. The method according to any one of claims 1 to 17,
Wherein the reaction chamber is not divided into separate parts. 19. The method according to any one of claims 1 to 18,
Wherein the fluidized bed reactor comprises an annular inner chamber formed between the reaction chamber wall and the outer shell,
The method comprises:
At least about 10 bar, at least about 15 bar, at least about 1 bar, at least about 20 bar, at least about 1.1 bar, at least about 20 bar, at least about 20 bar, From about 1 bar to about 20 bar, or from about 5 bar to about 20 bar, and less than the pressure in the reaction chamber. 20. The method according to any one of claims 1 to 19,
Up to at least about 500 캜, to at least about 600 캜, to at least about 650 캜, to at least about 700 캜, to at least about 750 캜, from about 600 캜 to about 800 캜, or from about 700 캜 to about 800 캜 &Lt; / RTI &gt; 1. A method for producing polycrystalline silicon by thermal decomposition of silane in a fluidized bed reactor having a reaction chamber and a distributor for distributing the gas into the reaction chamber,
Wherein the reaction chamber has a cross section through which the core region, the peripheral region and the feed gas pass, the fluidized bed reactor producing at least about 100 kg / hr of polycrystalline silicon per square meter of reaction chamber cross-
The method comprises:
Introducing a first feed gas comprising silane into the distributor to distribute a first feed gas into the core region of the reaction chamber, the reaction chamber containing silicon particles, the first feed gas comprising about 80 volumes Wherein the temperature of the first feed gas prior to introduction into the distributor is less than about 400 DEG C and the silane is thermally decomposed in the reaction chamber to deposit a significant amount of silicon on the silicon particles, ; And
Introducing a second feed gas into the distributor to introduce the second feed gas into the peripheral region of the reaction chamber wherein the concentration of silane in the first feed gas exceeds the concentration in the second feed gas, The pressure in the reaction chamber is at least about 3 bar.
&Lt; / RTI &gt; 22. The method of claim 21,
Wherein the reaction chamber has an annular wall and has a generally circular cross-section with a center and a radius R, wherein the core area has a radius of less than about 0.975R, less than about 0.6R, less than about 0.5R, , At least about 0.5R, at least about 0.6R, at least about 0.8R, or at least about 0.9R, said peripheral region extending from said central region to said annular wall. 23. The method of claim 21 or 22,
Wherein the temperature of the first feed gas prior to introduction into the distributor is less than about 350 占 폚, less than about 300 占 폚, less than about 200 占 폚, or less than about 100 占 폚. 24. The method according to any one of claims 21 to 23,
Wherein the temperature of the second feed gas prior to introduction into the distributor is less than about 400 占 폚, less than about 350 占 폚, less than about 300 占 폚, less than about 200 占 폚, or less than about 100 占 폚. 25. The method according to any one of claims 21 to 24,
The temperature of the second feed gas prior to introduction into the distributor is at least about 300 캜, at least about 350 캜, at least about 450 캜, at least about 550 캜, from about 300 캜 to about 600 캜, or from about 450 캜 to about 600 캜 , Way. 26. The method according to any one of claims 21 to 25,
The pressure in the fluidized bed reactor is at least about 4 bar, at least about 5 bar, at least about 10 bar, at least about 15 bar, at least about 20 bar, at least about 25 bar, from about 3 bar to about 25 bar, bar, method. 27. The method according to any one of claims 21 to 26,
At least about 4 bar, at least about 5 bar, at least about 10 bar, at least about 15 bar, at least about 20 bar, at least about 25 bar , From about 3 bar to about 25 bar, or from about 4 bar to about 20 bar. 28. The method according to any one of claims 21-27,
Wherein the volume-based concentration of the silane in the first feed gas is at least about 25% higher than the volume-based concentration of the silane in the second feed gas, or the volume-based concentration in the first feed gas is at least about 25% At least about 50%, at least about 75%, at least about 100%, at least about 150%, at least about 200%, or from about 25% to about 200%, from about 25% to about 100 % Or about 50% to about 200% higher. 29. The method according to any one of claims 21 to 28,
At least about 25%, at least about 50%, at least about 75%, at least about 85%, at least about 85%, or at least about 80% of the silane introduced into the fluidized bed reactor, At least about 95%, or about 100%, is introduced through the core region. 30. The method according to any one of claims 21 to 29,
Wherein particulate polycrystalline silicon is recovered from the fluidized bed reactor and wherein the mean average diameter of the particulate polycrystalline silicon is from about 600 microns to about 2000 microns or from about 800 microns to about 1300 microns. 31. The method according to any one of claims 21 to 30,
Wherein the average residence time of the gas introduced into the reaction chamber is less than about 20 seconds, less than about 12 seconds, less than about 9 seconds, less than about 4 seconds, less than about 1 second, or about 0.1 seconds to about 20 seconds. 32. The method according to any one of claims 21 to 31,
At least about 150 kg / hr of silicon per square meter of reaction chamber cross-section is deposited on the silicon particles, or at least about 250 kg / hr, at least about 300 kg / hr, at least about 500 kg at least about 1000 kg / hr, at least about 2000 kg / hr, at least about 3000 kg / hr, at least about 4000 kg / hr or about 100 kg / hr to about 5000 kg / hr, From about 250 kg / hr to about 5000 kg / hr, from about 100 kg / hr to about 4000 kg / hr, or from about 100 kg / hr to about 1000 kg / hr of silicon is deposited on the silicon particles. 33. The method according to any one of claims 21 to 32,
The second feed gas comprises less than about 80 vol% silane, less than about 60 vol%, less than about 40 vol%, less than about 20 vol%, less than about 15 vol%, less than about 10 vol%, less than about 5 vol% From about 2 vol% to about 80 vol%, from about 5 vol% to about 80 vol%, from about 5 vol% to about 25 vol%, or from about 2 vol% to about 20 vol%. 34. The method according to any one of claims 21 to 33,
Wherein the second feed gas essentially comprises compounds other than silane. 35. The method according to any one of claims 21 to 34,
Wherein the second feed gas essentially comprises at least one compound selected from the group consisting of silicon tetrachloride, hydrogen, argon and helium. 36. The method according to any one of claims 21 to 35,
Wherein the first feed gas comprises less than about 60 vol% silane, less than about 40 vol%, less than about 20 vol%, less than about 15 vol%, less than about 10 vol%, less than about 5 vol%, about 2 vol% 60 vol%, about 5 vol% to about 60 vol%, about 5 vol% to about 25 vol%, or about 2 vol% to about 20 vol% silane. 36. The method according to any one of claims 21 to 36,
The total concentration of silane in the feed gas introduced into the reaction chamber is less than about 80 vol%, less than about 60 vol%, less than about 40 vol%, less than about 20 vol%, less than about 15 vol%, less than about 10 vol% From about 5% to about 80%, from about 5% to about 25%, or from about 2% to about 20% by volume. 37. The method according to any one of claims 21 to 37,
Wherein the reaction chamber is not divided into separate parts. 39. The method according to any one of claims 21 to 38,
Wherein the fluidized bed reactor comprises an annular inner chamber formed between the reaction chamber wall and the outer shell,
The method comprises:
At least about 10 bar, at least about 15 bar, at least about 1 bar, at least about 20 bar, at least about 1.1 bar, at least about 20 bar, at least about 20 bar, From about 1 bar to about 20 bar, or from about 5 bar to about 20 bar, and less than the pressure in the reaction chamber. 40. The method according to any one of claims 21 to 39,
To at least about 500 캜, to at least about 600 캜, to at least about 650 캜, to at least about 700 캜, to at least about 750 캜, from about 600 캜 to about 800 캜, or from about 700 캜 to about 800 캜 / RTI &gt;

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